In the Etymologies and earlier, the roots √ULU “pour, flow” and √LU “time” are listed separately. On PE17/168, the word Q. lúmë¹ “time” is listed as a derivative of √ULU “flow”, however. It may be that LU in an inversion of that root, with the sense “time” coming from “flow of time”.
Related
LU “*(flow of) time” may be an inversion of √UL “pour (out), flow”